1. Field of the Invention
The present invention relates to a system for controlling intake air pressure in an internal combustion engine provided with a mechanical supercharger operated by the crankshaft of the engine.
2. Description of the Related Art
Known in a prior art reference is an internal combustion engine provided with a mechanical supercharger connected directly or via a clutch device to the engine crankshaft. The engine rotation is transmitted directly or via the clutch to the supercharger for attaining the supercharging operation.
The supercharged engine usually requires an increased voltage for an ignition (hereinafter, ignition requirement voltage) when the engine condition is changed by an acceleration thereof. The increase in the ignition requirement voltage is very large under an acceleration condition wherein the engine is accelerated from a preceding deceleration condition with a fuel cut, since the spark plugs are cold. To obviate this difficulty, as disclosed in Japanese Unexamined Patent Publication No. 59-15626, a system has been proposed wherein the supercharger is controlled so that the supercharging effect is gradually increased when a clutch for controlling the supercharger is changed from the disengaged position to the engaged position. After a lapse of a predetermined time from the clutch position changeover, the supercharger is switched to full operation. This prior art is disadvantageous in that it has a poor response in engine power during an acceleration, since there is always an delay in the switching of the operation of the supercharger when the engine begins to accelerate.
This prior patent also suffers from another drawback in that a sharp increase in the engine torque can not be obtained when the driver has fully depressed the accelerator pedal to attain a rapid acceleration, causing an inferior driveability during such a rapid acceleration.